Airborne atmospheric research using mid-infrared laser spectroscopy

• Published in: SPIE Proceedings, Quantum Sensing and Nanophotonic Devices VI
• Other Authors: Fried, Alan (author), Razeghi, Manijeh (editor), Weibring, Petter (author), Sudharsanan, Rengarajan (editor), Richter, Dirk (author), Brown, Gail (editor), Walega, James (author)
• Format: Article in Journal/Newspaper
• Language: English
• Published: SPIE 2009
• Subjects: Arctic
• Online Access: http://nldr.library.ucar.edu/repository/collections/OSGC-000-000-002-915; https://doi.org/10.1117/12.803634

Over the past two decades mid-infrared laser spectroscopy has been increasingly utilized during airborne atmospheric studies to improve our understanding of atmospheric processes and transformations. Enhancing such understanding requires a suite of ever more sensitive, selective, versatile, and fast instruments that can measure trace atmospheric constituents at and below mixing ratios of 100-parts-per-trillion-by-volume. Instruments that can carry out such measurements are very challenging, as airborne platforms vibrate, experience accelerations, and undergo large swings in cabin temperature and pressure. These challenges notwithstanding, scientists and engineers at the National Center for Atmospheric Research (NCAR) have long been employing mid-infrared absorption spectroscopy to make atmospheric measurements of important trace gases like formaldehyde (CH₂O) on a variety of airborne platforms. The present paper discusses a new airborne spectrometer based upon a difference frequency generation (DFG) mid-IR laser source that was first deployed in 2006. Many of the fundamental components and concepts of this spectrometer closely follow those incorporated in our liquid-nitrogen cooled tunable lead-salt diode laser system, successfully employed for airborne CH₂O measurements over the past 10 years. However, a number of significant modifications were incorporated in the new DFG spectrometer and these will be briefly discussed here along with system performance. The DFG spectrometer was recently deployed during the 2008 Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) campaign, and specific examples of its performance from this study will be discussed, as will prospects for the detection of other trace gases.